Typically, a data transmission system may include differential signaling for transmission of serial data from a transmitter (TX) circuit to a receiver (RX) circuit. Such a transmission of serial data may be performed over a differential channel, through a high definition interface, such as a High-Definition Multimedia Interface (HDMI), a Mobile High-Definition Link (MHL), Display Port, Universal Serial Bus (USB), and the like. In certain scenarios, the TX circuit may correspond to a portable device, such as a laptop and a mobile phone, which is powered through an internal battery. Further, the RX circuit may correspond to a non-portable or wall-mounted device, such as a television (TV), a monitor, or other such display device, which is powered through an external power socket.
In such a data transmission system, the overall power consumption correspond to a combined power consumption in the TX circuit and the RX circuit. Generally, the receiver circuit consumes more power, such as 70 to 80 mW, which is about three to four times larger, than the power consumed by the transmitter circuit, such as 20 to 30 mW per channel. The transmitter circuit includes various internal circuitries, such as a data serializer circuit, a phase locked loop (PLL) circuit, a pre-driver circuit, and a common mode logic (CML)-based driver circuit. The driver circuit, terminated to the RX circuit supply, consumes power from the power supply of the RX circuit.
Currently, various techniques are utilized for designing the transmitter circuit that consumes less power. In accordance with one of such techniques, a low-power transmitter circuit has been designed that uses an external 1V core power supply for the pre-driver circuit, which results in an multi-fold increase in the differential switching pair area and current source area in the corresponding driver circuit due to limited headroom compared to when the pre-driver is powered from a 3.3V IO supply. Further, the increase in the differential pair area and the current source area of the driver circuit leads to large capacitance on the input and common source node of the differential pair in the driver circuit, resulting in reduction of speed of operation and a large dynamic leakage of the tail current of the driver circuit, thereby reducing effective current in the driver circuit. In such a technique, power consumption by the pre-driver circuit is reduced due to the utilization of external 1V core power supply; however, there is a speed penalty and the power consumption by the driver circuit is substantially increased from the power supply of the RX circuit for the same output swing levels.
In accordance with another technique, the pre-driver circuit uses the external 1V core power supply and an AC coupling capacitor that is used to couple the pre-driver circuit output to the input common mode voltage of the driver circuit. This technique results in better headroom, however the use of the AC coupling capacitor adds parasitic capacitance loading on the output of the pre-driver circuit, thereby loading the pre-driver circuit and hence resulting in higher power consumption and lower speed.
In accordance with yet another technique, the transmitter circuit uses a common source node of the driver circuit as the power supply for the pre-driver circuit and other preceding circuitries, such as the data serializer circuit, of the transmitter circuit. However, this technique adds a substantial capacitance on the common source node of the driver circuit. The added capacitance on the common source node results in the reduction of the output impedance of the current source, leading to degradation in the quality and speed of the CML switching at the output of the driver circuit.
In accordance with yet another technique, the transmitter circuit may utilize external 3.3V power supply to provide sufficient margin on the driver circuit instead of external 1V core power supply. Due to the usage of the external 3.3V power supply in the TX circuit for pre-driver circuit, the driver circuit operates with sufficient headroom, but the pre-driver circuit current consumption increases. In such a case, usually the pre-driver circuitries consumes approximately 70 to 80 percent of the total power consumed by the transmitter circuit.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to those skilled in the art, through a comparison of the described systems with some aspects of the present disclosure, as set forth in the remainder of the present application and with reference to the drawings.